Hazardous Pollutants & Air Impacts

Downwash leads to greater pollution levels near the ground level, downwind of the smoke stacks. In order to prevent downwash, EPA created rules to regulate stack height. The EPA formula is that the stacks should be 2.5 times the building height - something called the "good engineering practice" stack height. According to this formula, Dominion Cove Point LNG's stack height should be 113.5 feet. Dominion's stack height is 63.5 feet lower than the recommended height, which means the downwash increase in ground level pollution will be severe. An excellent review titled Stack Height and Air Pollution by James Long (below), shows how the air pollution will be further concentrated at ground level due to the lowered stacks, and it also touches on how the air flow in this topographic area will further concentrate the pollution. 

Natural gas pipeline compressors operate around the clock, and they emit air pollution 24 hours a day, seven days a week. The pollution comes from large engines needed to drive the compressors. Of course, the cheapest fuel available on a pipeline is natural gas. The pipeline that will enter Charles Station will contain “wet gas,” or gas that contains a higher composition of hydrocarbons such as ethane and butane, which cause incomplete combustion of the natural gas and increased emissions of a number of chemicals through normal operations. Toxic air emissions will include formaldehyde, benzene, toluene, ethylbenzene, xylene, hydrogen disulfide, methane, and other pollutants. As an example, emissions per year of just four kinds of air pollutants would be equivalent to that emitted by 887 idling tractor-trailer trucks: 41 tractor-trailer trucks worth of nitrogen oxide (NOx), 53 tractor-trailer trucks worth of volatile organic compounds (VOCs), 132 tractor-trailer trucks worth of carbon monoxide (CO), and 661 tractor-trailer trucks worth of ambient particulate air pollution (PM2.5).

Two other sources of pollutant emissions from compressor stations are from fugitive emissions, or leaks (see video below), and blowdowns. A blowdown is a complete venting of the natural gas within a compressor or pipeline to the atmosphere, to reduce pressure and empty the system. These typically occur either during an emergency shutdown, or during routine station maintenance.


Blowdowns are very loud events, and they are associated with enormous amounts of pollution emitted in relatively short periods of time. A single compressor blowdown can release up to 15,000 cubic feet of methane to the atmosphere, along with any other products in the pipeline, including chemicals remaining from the fracking process.

These periods of extreme exposure greatly increase the public health risks associated with compressor stations, compared with other stationary sources of pollution that do not exhibit such large swings in emissions. Acute health effects have been reported  during blowdowns, such as burning eyes or throat, skin irritation, headaches, and nosebleeds. These health risks could be especially severe near the proposed Charles Station facility because an unusually large number of blowdowns are scheduled to occur each year. Scheduled “startup/shutdown” blowdowns will occur at least one hundred times each year, and unplanned emergency blowdowns will take place in addition to these 100 annual events. 

Routine emissions from compressor stations are significant; 60–75 % of the estimated damages (mostly health problems) from all natural gas activities result from compressor station activities. 

Some of the toxic chemicals that pipeline compressor stations emit include:

  • Nitrogen oxides (NOx), which are associated with respiratory disease. 

  • Volatile organic compounds (VOCs) are toxins to the nervous system and have significant cognitive and behavioral effects. They are known liver toxins, reproductive toxins and are toxic to a developing fetus. All are skin toxins.

  • Ozone is formed when nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs) react in the presence of heat and sunlight. Ozone is a powerful oxidant which damages respiratory tissues in animals, and plants, even at extremely low concentrations. Ozone is a potent respiratory hazard and pollutant near ground level. This area is already in violation of federal ozone standards.

  • Benzene and formaldehyde, which cause cancer.

  • Sulfur dioxide (SO2) is associated with respiratory & neurological illness, and death.

  • Particulate matter is of small size and carries toxic pollutants deep into the lungs, and is a carcinogen. 

The gas flowing through natural gas pipelines carries radon, the radioactive gas. As radon decays within the pipeline, it breaks down into the radioactive elements polonium and lead, which accumulate along the interior of the pipes. Lead causes neurologic and hematologic toxicity, and death; polonium causes cancer and death. There is a concern that these radioactivity levels will pose a risk to both workers at the compressor stations and, potentially, also to the residents. The gas in the pipelines also contains Polychlorinated Biphenyls (PCBs), a known environmental toxin and persistent organic pollutant. The International Agency for Research on Cancer (IARC) rendered PCBs as definite carcinogens in humans.

The Maryland Department of the Environment (MDE) is responsible for reviewing Dominion Cove Point LNG’s application for an Air Quality Permit to Construct. As part of that permitting process, MDE held a hearing on the evening of Wednesday, March 28th. It was very well attended by residents of both Prince George’s and Charles Counties, with standing room only. Testimony against the permit continued through the evening, some of it quite moving. Approximately 60 people testified with concerns about the project, and more than double that number were in attendance at the hearing. During the three-and-a-half hours of testimony, multiple problems with Dominion’s permit application began to emerge. One glaring omission is that the numbers used by Dominion in modeling for the permit do not fully account for emissions from blowdowns. Blowdowns are the single greatest source of emissions from compressor stations. MDE’s draft permit fails to model the one-hour nitrogen oxide emissions associated with blowdowns “due to the infrequent nature of start-up/shutdown events,” which MDE says will only occur for 16.7 hours a year. Yet MDE elsewhere states in its March 2018 modeling summary that the start-up/shutdown events will last for at least double that number of hours each year (2,000 minutes per year, or 33.3 hours). 

There are multiple other problems with the permit, not the least of which includes obtaining background ambient air quality data from a site in Arlington, VA and not from the proposed site area. Additional concerns about incomplete and inconsistent emissions and monitoring of data were expressed by numerous speakers at the air permit hearing. For example, Dominion is permitted 30 days to fix any leaks at the station, and we will not notice leaks because the gas is not going to be odorized. 

Additional Information and Resources


MDE Air Permits Info & News
Air Quality Talking Points (pdf)

Stack Height and Air Pollution by James Long (pdf)
WilliamsLathrop Compressor naked eye and FLIR (video) Thanks to Kelly Canavan of  AMP Creeks for sharing this video

This gas-fired pipeline compressor station that Dominion Cove Point LNG is proposing to install in our neighborhood will emit many different hazardous air pollutants. No health impact assessment for this community has been performed, despite the predicted health impacts for those most susceptible to hazardous air pollutants: pregnant women, children, and the elderly. The air pollution in our community would be worse than for many other communities near pipeline compressor stations because this proposed compressor station is a particularly large one -- larger than all compressor stations in New York, for example. Plus, this station would be located in a geographic depression where pollution collects. Finally, the planned smoke stack height was lowered from 83 feet to 50 feet, which will further increase the amount of air pollution lower to the ground.

The height of the exhaust stacks, which have been lowered to 50 ft. in order to preserve the view from Mount Vernon, is a serious problem. The stack height is going to be lower than the tree canopy, just 4.6 feet higher than the proposed pipeline compressor building. When smoke stacks are not sufficiently taller than the buildings that surround them, air pollutants tend to get trapped in recirculating paths downwind of the buildings, in a phenomenon called "downwash."

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